Microscopic polar clusters can play an important role in the phase transition of ferroelectric perovskite oxides such as $\mathrm{BaTi}{\mathrm{O}}_3$, which have shown coexistence of both displacive and order-disorder dynamics, although their topological and dynamical characteristics are yet to be clarified. Here, we report sharp increases in the widths and intensities of Bragg peaks from a $\mathrm{BaTi}{\mathrm{O}}_3$ single crystal, which are measured in situ during heating and cooling within a few degrees of its phase transition temperature $T_C$, using the neutron time-of-flight Laue technique. Most significantly sharper and stronger increases in peak widths and peak intensities were found to occur during cooling compared to that during heating through $T_C$. A closer examination of the Bragg peaks revealed their elongated shapes in both the paraelectric and ferroelectric phases, the analysis of which indicated the presence of microdomains that have correlated $\langle 111\rangle$-type polarization vectors within the {110}-type crystallographic planes. No significant increase in the average size of the microdomains $(\sim 10\mathrm{nm})$ near $T_C$ could be observed from diffraction measurements, which is also consistent with small changes in the relaxation times for motion of Ti ions measured with quasielastic neutron scattering. The current observations do not indicate that the paraelectric-ferroelectric phase transition in $\mathrm{BaTi}{\mathrm{O}}_3$ is primarily caused by an increase in the size of the microscopic polar clusters or critical slowing down of Ti ionic motion. The sharp and strong increases in peak widths and peak intensities during cooling through $T_C$ are explained as a result of microstrains that are developed at microdomain interfaces during paraelectric-ferroelectric phase transition.

• Received 18 August 2015
• Revised 17 September 2015

DOI:https://doi.org/10.1103/PhysRevB.92.174103